1. Field of the Invention
The present invention relates to a steam reflow apparatus and a steam reflow method for soldering an electronic component mounted on a substrate by high-temperature superheated steam.
2. Description of the Related Art
A heated body such as a substrate on which an electronic component is mounted is fed to a reflow apparatus, and soldering is performed on the heated body. Such heated body may be collectively called a “substrate”. A heating furnace of the conventional reflow apparatus includes a preheating zone, a uniform heating zone, a melting zone, and a cooling zone. While the substrate is conveyed by a conveyor, the substrate is heated from ordinary temperature to about 150° C. or higher in the preheating zone, and is fed to the uniform heating zone. After the substrate is heated for a while at about 150° C. or higher in the uniform heating zone, the substrate is fed to the melting zone. Then, the substrate is rapidly heated to about 230° C. higher than or equal to a solder melting point (about 219° C. though the melting point varies depending on a kind of solder) in the melting zone, and the solder is melted. Then, after the substrate is fed to the cooling zone and is cooled by a fan or the like and the melted solder is solidified, the substrate is carried out to the outside of the heating furnace.
When the substrate is heated in the heating furnace as described above in air reflow, a surface of solder is oxidized by oxygen in air activated at a high temperature, and wettability of the solder is decreased. Hence, nitrogen reflow for filling the inside of the heating furnace with nitrogen gas which is inert gas and performing soldering is known. The nitrogen reflow can prevent oxidation of the surface of the solder even when the substrate is heated at the high temperature. However, the nitrogen reflow has a problem of increasing a cost since a large amount of nitrogen gas is consumed.
Hence, instead of the nitrogen reflow, steam reflow for performing soldering by superheated steam (hereinafter simply called “steam”) with a high temperature of 100° C. or higher is proposed (JP-A-2008-270499 and JP-A-2011-82282 as Patent References 1 and 2).
Patent Reference 1: JP-A-2008-270499
Patent Reference 2: JP-A-2011-82282